Sharpening camber with WorkSharp

[Dan T Jones]

As I get into this plane world I see I need to camber the blades. Do any of you do this on a WorkSharp and if so how do you go about it?
Thank you.
Dan

[Jim Koepke]

As I get into this plane world I see I need to camber the blades. Do any of you do this on a WorkSharp and if so how do you go about it?
Thank you.
Dan

Needing to camber blades is more of an opinion or an option than a fact.

I use a Vertas Mk.II Power Sharpening System. To camber a blade for my scrub plane the blade is turned through an arc on a medium grit abrasive disk.

I could not tell you the radius or depth differential on my scrub plane blade.

If you desire a camber, it doesn't take a lot to eliminate tracks left by the blade. With thin shavings the camber only needs to lift the edges of the blade a touch more than the shaving thickness to be effective.

jtk

[Prashun Patel]

I used to when I strictly used the WS. Now, I use the WS for bevel setting and my waterstones for honing. So, I prefer to set the bevel as straight as possible, and then camber during the honing. Don't go by me, though, because I haven't mastered my cambering yet; it's just the way I'm currently practicing on.

I top grind with the WS. This allows me to use my MKII jig to set the angle. The MKII with the regular roller has enough play that if you press on either side of the blade, you can get the wheel to hit the corners harder than the center. The mistake I made when cambering at first was pressing too hard on the corners. In my experience, you really just need the line to curve slightly from the center to the edge, not be straight and then drop off drastically; so it's more of a gentle rocking from left to right than pressing and tipping (thanks for the tips on this, Derek Cohen).


The WS is super aggressive (if your wheels are clean ;)) so let the wheel do the work; if you try to press into it, you'll risk your bevel going off square.

Last, consider getting "Cheap Chinese" diamond lapidary plates from your favorite online auction site. These last a good long while, and will really speed you up.

[Curt Putnam]

As mentioned already, I use the wide blade adapter (table) to grind and not the port. Since the outer edge of the disk goes faster than the middle, you can achieve a curved edge by rotating your honing jig about the centerline. You can also simply rock the jig while staying on the centerline, or, you can do some of both. I wouldn't try it freehand.

[Patrick Chase]

Here we go again :-)



If you desire a camber, it doesn't take a lot to eliminate tracks left by the blade. With thin shavings the camber only needs to lift the edges of the blade a touch more than the shaving thickness to be effective.


That's true if you're just cambering to avoid tracks as with a smoother or jointer (and in that case you don't need full-width camber at all as you say - just relieving the edges is sufficient).

It's not true if you're cambering to take efficient roughing cuts as with a scrub, fore, or a jack used for roughing. In those cases you want for a constant radius of anywhere from 3" (scrub) to ~8" (fore) across the entire width.

Question for the OP: Why do you need camber? Is it just to avoid tracking, or do you use planes to rough stock?

[Dan T Jones]

Yes, I am simply interested in the idea of using a smoother instead of sanding. So, I'm understanding just a slight rounding at the edges.
Thanks for the help.
Dan

[Patrick Chase]

Yes, I am simply interested in the idea of using a smoother instead of sanding. So, I'm understanding just a slight rounding at the edges.
Thanks for the help.
Dan

Yep.

At the very most you need to relieve the corners by the depth of cut divided by the cosine of the bed angle. If the blade is parallel to the sole then that puts the corners in the same plane as the sole, where they can't possibly cut and leave a track. So for example if you take 4-mil smoothing cuts with a 45-deg bench plane you'd relieve the corners by 4/cos(45) = ~6 mils.

In reality if your technique is reasonable you can get by with quite a bit less than that. All that matters is that the corner never cuts deeper than the track left by the previous/adjacent pass, and couple mils usually does the trick.

[Dan T Jones]

OK, no point in hiding ignorance. What's a mil?

[Jim Koepke]

So for example if you take 4-mil smoothing cuts with a 45-deg bench plane you'd relieve the corners by 4/cos(45) = ~6 mils.

Can that be done using a story stick? I didn't realize woodworking had so much math.


OK, no point in hiding ignorance. What's a mil?

Something most people ignore when putting a camber on a blade. (For future reference, one mil is usually 0.001" but since there are people from all around the globe here one mil could be one millimeter.)

jtk

[Patrick Chase]

First off, my apologies for the tone of my previous post. When I said "here we go again" I meant that we were revisiting a previously contentious topic, but I realize now (after some help - thanks!) that it could also be interpreted as referring to Jim. Sorry about that!


Can that be done using a story stick?

If I were to measure such a thing I'd use shim stock feeler gauges, but...


I didn't realize woodworking had so much math.

The purpose of my post wasn't to say that you should be accurate to the 1/1000th (obviously you don't need that), but rather to illustrate the useful range. I've seen people put ridiculous amounts of relief on their blade corners because they don't understand when it ceases to be beneficial.

I've also seen people use unworkably low amounts of relief on low-angle bevel-up blades because they don't realize that you need about 3.5x as much relief to get the same effect (same amount of "tracking avoidance") with a 12 deg bed as you do with a 45 deg bed.

The equation concisely captures both (or would if I'd gotten it right), but I'd love to see a better way to compactly explain it.

BTW, I butterfingered. If the bed angle starts at 0 when it's flat, then the equation is max_useful_relief = cut_depth/sin(bed_angle). For a common-pitch plane they happen to be the same, so the 6-mil number was correct.


For future reference, one mil is usually 0.001" but since there are people from all around the globe here one mil could be one millimeter.

I've lived in Europe for a couple years, and worked with teams from all over the world. I've never seen "mil" used as an abbreviation for any unit other than 1/1000". Millimeter is always abbreviated as "mm".